Each game has a reported development cost which, importantly, excludes marketing spend. So this is mostly the cost of salaries and various forms of overhead such as tools. When costs were reported in currencies other than the dollar (Euro, yen, even zlotys) I went back to the year of release, and converted the cost to a dollar value using the exchange rate prevailing in December of that year. I then took all dollar values and adjusted them for inflation so that we are comparing actual cost in today’s money.